This invention relates to novel crosslinkable compositions comprised of epoxidized monohydroxylated diene polymers, amino resins and reinforcing agents. More specifically, the invention relates to the use of particular epoxidized monohydroxylated polydiene polymers in crosslinking with amino resins to produce products which are useful in a variety of reinforced compositions for adhesives, sealants and coatings. The invention also relates to a process for making high quality compositions with these three normally incompatible components.
Hydroxy functional polydiene polymers are well known. It has been shown that formulations containing these polymers, a melamine resin, and an acid catalyst can be cured by baking under normal bake conditions. Most of these polymers are homopolymers of one diene or another. For example, monohydroxylated polybutadienes are known in the art for use in adhesive formulations. U.S. Pat. No. 4,242,468 describes solventless polyurethane coatings having improved flexibility resulting from incorporation of monohydroxylated polybutadienes. Epoxidized versions of hydroxylated polybutadienes are known as well. Low viscosity epoxidized polydiene polymers are also known, especially for use in adhesives. Such polymers are described in commonly assigned U.S. Pat. Nos. 5,229,464 and 5,247,026.
Compositions based on functional polydiene polymers cured with a crosslinking agent are usually fairly soft and, although they can be very useful in some applications, have limited adhesion. Attempts to increase hardness and adhesion by increasing crosslink density with a reinforcing agent, such as a low molecular weight diol or triol, and higher levels of crosslinking agent were unsuccessful because the reinforcers and crosslinkers are relatively polar and so are incompatible with the relatively nonpolar polydiene polymers. Incompatibility of the components leads to poor properties, such as gloss, in the cured composition or, even worse, the compositions may phase separate upon standing. This invention provides a method for making compatible compositions from these components and the novel compositions themselves.